Fobless (and only) key unable to start the car (or switch off alarm) after replacing car's battery

[londonrizzo]

Hi!

I'm desperate. I just replaced the battery of my 1993 Audi 100 2.5 TDI, but now the alarm won't stop, and I only have a fobless key.

Does anybody know how to start the car/disarm the alarm/immobiliser?

Hope anybody out there solved this in the past without having to order new keys.

Thanks!